A. A. Bessonov

Synthesis and structure of crystalline complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid. Complexation in solution and spectral studies

Complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid, C12H6N2(COOH)2 (H2PDA), of the compositions [(NpO2)2(PDA)(H2O)3]·H2O (I), (NH4)2[NpO2(PDA)]2·3H2O (II), and [C(NH2)3]2[NpO2·(PDA)]2·4H2O (III) were synthesized. The Np atoms in the crystal lattices of all the compounds have the pentagonal bipyramidal coordination surrounding, with the [C12H6N2(COO)2]2− anions acting as chelate-bridging N,O-donor ligands. In the structure of I, two crystallographically independent NpO2+ dioxocations participate in the cation-cation interaction leading to the formation of tetrameric cation-cation complexes. The nonequivalence of the Np atoms is manifested in splitting of the main absorption band of Np(V) in the electronic spectrum of solid compound I. The structures of II and III are based on dimeric anionic complexes [NpO2(C12H6N2(COO)2)]22−. Only one kind of complexes, NpO2(PDA)−, was detected in the solution, and high value of the concentration stability constant β, ∼1012 L mol−1, is due to tetradentate coordination of the ligand.

Preparation of Np, Pu, and U dioxides in nitric acid solutions in the presence of hydrazine hydrate

Heating of nitric acid solutions of Np and Pu (∼90°C) in the presence of hydrazine hydrate (HH) leads to the formation of their hydrated dioxides in solution, transforming into crystalline dioxides at 300°C. Thermolysis of a mixed solution of U, Np, and Pu nitrates under the same conditions initially yields hydrated (U,Np,Pu)O2·nH2O, which on heating in air to ∼300°C transforms into a crystalline solid solution of (U,Np,Pu)O2. This method for stabilization of U dioxide in the presence of Pu in an oxidizing atmosphere can be used for preparing (U,Pu)O2 solid solutions of variable composition. This procedure shows doubtless prospects as a simple, efficient, and relatively low-temperature method for the production of MOX fuel for fast reactors.

Interaction of U(VI), Np(VI), and Pu(VI) with picolinic (2-pyridinecarboxylic) acid: Complexation in aqueous solutions and synthesis, spectra, and thermal properties of complexes [CH6N3][AnO2(C6H4NO2)3] (An = U, Np, Pu)

Complexation of actinides(VI) (U, Np, Pu) with picolinic acid C6H5NO2 (HPic) in solution was studied by spectrophotometry. In particular, data on the Np(VI) complexation were obtained for the first time. The complexes [AnO2(HPic)]2+, [AnO2(Pic)]+, [AnO2(Pic)2], and, presumably, [AnO2(HPic)(Pic)]+, and also mixed picolinate-hydroxide complexes can exist in the solution under different conditions. The stability constants of the complexes were estimated. A series of crystalline actinide(VI) picolinate complexes Gu[AnO2(Pic)3] (An = Np, Pu; Pic is picolinate ion, Gu is guanidinium ion) were synthesized, and their structure was determined. The spectra and thermal behavior of the complexes are discussed.

Synthesis of M(NpO 4 ) 2 · n H 2 O (M = Mg, Ca, Sr, Ba) Using Н 3 ВО 3 Solutions and Properties of These Salts

Two procedures for preparing the compounds M(NpO4)2·nH2O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M3(NpO5)2·nH2O (M = Ca, Sr, Ba) are treated with excess 0.5 M H3BO3 with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO4)2·nH2O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO4 (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO23+ cations and bridging O atoms. New data on the properties of the compounds M3(NpO5)2·nH2O with M = Ca, Sr, and Ba were also obtained.

Absorption of nitrogen hemioxide in aqueous solutions of gas treatment systems upon dissolution of UN in nitric acid

The absorption of N2O from an air flow in various aqueous solutions at 293–298 K was studied. The maximal N2O absorption under the experimental conditions is reached for water (~22–24%) and saturated solution of K2Cr2O7 in concentrated H2SO4 in the presence of Al2O3 and without it (~34 and ~30%, respectively). In concentrated HNO3 and NH4OH solutions and in 1.0 M NaOH and N2H4·nH2O solutions, the degree of the N2O absorption varied from ~7.5 to ~11.5%. Similar degree of absorption was obtained with 0.5 M (NH2)2CO (~11%). In the other solutions tested, the degree of the N2O absorption did not exceed ~4.0%.

Synthesis, X-ray diffraction analysis, and spectral properties of the double cesium neptunium nitrite Cs3[NpO2(NO2)4] and thiocyanate Cs4[NpO2(NCS)5]·2.5H2O

The structure and spectral properties of the Np(V) nitrite and thiocyanate complexes Cs3[NpO2· (NO2)4] and Cs4[NpO2(NCS)5]·2.5H2O were studied. In the structure of Cs3[NpO2(NO2)4], two independent Np atoms occupy special positions and have similar oxygen surrounding in the form of hexagonal bipyramids. The equatorial planes of the bipyramids are formed by the oxygen atoms of four independent nitrite ions, two of which are bonded in the monodentate fashion and two, in the bidentate fashion. There are three independent Cs atoms in the structure; their coordination surrounding is constituted by the O atoms of NpO 2+ cations and NO 2- anions. The Cs(1) atom has the coordination surrounding in the form of a 9-vertex polyhedron; Cs(2), in the form of a 10-vertex polyhedron; and Cs(3), in the form of an 8-vertex polyhedron. In the structure of Cs4[NpO2(NCS)5]·2.5H2O, the Np atom has the coordination surrounding in the form of a pentagonal bipyramid with the equatorial plane formed by the nitrogen atoms of five independent NCS– ions. There are four independent Cs cations in the structure; their coordination surrounding is constituted by the O, N, C, and S atoms. The surrounding of the Cs(1), Cs(2), Cs(3), and Cs(4) atoms can be described as 11-, 14-, 12-, and 9-vertex polyhedra, respectively. The IR and electronic absorption spectra of the compounds are presented.

Carbon-containing sorbents for removing volatile radioactive iodine compounds from the water vapor-air medium

The sorption of CH3131I and 131I2 from a water vapor-gas medium onto various grades of activated carbon was studied. All the sorbents tested exhibit high ability to take up 131I2. The 131I2 uptake exceeds 99.95% at 60°C and contact time of the gas phase with the sorbent τ = 0.5–0.7 s. The ability of the sorbents based on activated carbon to take up CH3131I strongly depends on the sorbent particle size. High ability to take up CH3131I from a water vapor-air flow is preserved only for cylindrical particles 1.0 mm in diameter and 1.0–2.0 mm long. Activated anthracite, like activated carbon with cylindrical particles 3.5 mm in diameter and 3.0–9.0 mm long, exhibits low performance in CH3131I uptake. The degree of localization of CH3131I does not exceed 40% at 60°C and τ = 0.5–0.7 s.